Method and apparatus for performing a handover in an evolved universal terrestrial radio access network

ABSTRACT

A method and an apparatus for performing a handover in an evolved universal terrestrial radio access network (E-UTRAN) are disclosed. A wireless transmit/receive unit (WTRU) sends a measurement report to a source evolved Node B (eNB), and receives a handover command from the source eNB. The WTRU initiates reception and processing of a primary broadcast channel (P-BCH) at the target cell after receiving the handover command. The WTRU then sends a random access preamble to the target eNB, receives a random access response from the target eNB, and sends a handover complete message to the target eNB. The reception and processing of the P-BCH may be initiated immediately after receiving the handover command or after sending the handover complete message. The WTRU may apply default configuration or source cell configuration in the target cell until a target cell SFN and/or P-BCH information are acquired.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/670,657, filed Nov. 7, 2012, which is issuing as U.S. Pat. No.8,989,143 on Mar. 24, 2015, which is a continuation of U.S. patentapplication Ser. No. 12/492,469, filed Jun. 26, 2009, which issued asU.S. Pat. No. 8,331,326 on Dec. 11, 2012, which claims the benefit ofU.S. Provisional Application Ser. No. 61/076,943 filed Jun. 30, 2008,the contents of all of which are incorporated by reference as if fullyset forth herein in their respective entirety, for all purposes.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

A handover is a process of transferring an ongoing call or data sessionfrom one cell to another. Conventionally, a wireless transmit/receiveunit (WTRU) assisted network controlled handover is implemented suchthat a WTRU measures a signal strength of neighboring cells and aserving cell and sends a measurement report to the network. The networkthen determines whether to perform the handover to another cell, (i.e.,a target cell).

FIG. 1 is a signaling diagram of a handover process 100 in the thirdgeneration partnership project (3GPP) long term evolution (LTE) network(intra-mobility management entity (MME)/serving gateway handoverprocedure). The source evolved Node-B (eNB) configures the WTRUmeasurement procedures according to the area restriction information(step 102). The WTRU sends a measurement report in accordance with therules set by system information, specification, etc. (step 104). Thesource eNB makes a handover decision based on the measurement report(step 106). The source eNB issues a handover request message to a targeteNB passing necessary information to prepare the handover at the targeteNB (step 108). Admission control may be performed by the target eNB(step 110). Once the target eNB decides to admit the WTRU, the targeteNB prepares handover with L1/L2 and sends a handover requestacknowledgement message to the source eNB (step 112). The handoverrequest acknowledgement message includes a transparent container to besent to the WTRU as a radio resource control (RRC) message. The sourceeNB sends a handover command to the WTRU (step 114).

Upon receipt of the handover command, the WTRU detaches from the sourcecell and synchronizes to the target cell and accesses the target cellvia an RACH following a contention-free procedure if a dedicated RACHpreamble was indicated in the handover command or following acontention-based RACH procedure if no dedicated RACH preamble wasindicated in the handover command (step 116). The target eNB sends arandom access response with uplink allocation and timing advance valuefor the WTRU (step 118). The WTRU then sends a handover complete messageto the target eNB (step 120). A normal operation starts between the WTRUand the target eNB thereafter.

A WTRU needs to know a system frame number (SFN) after handover for itsnormal operation in the target cell. Especially, both discontinuousreception (DRX) and reception of dynamic broadcast channel (D-BCH)require the WTRU to have the knowledge of SFN. Therefore, an efficientmethod would be desirable to handle SFN during and after handover.

SUMMARY

A method and an apparatus for performing a handover in an evolveduniversal terrestrial radio access network (E-UTRAN) are disclosed. AWTRU sends a measurement report to a source eNB, and receives a handovercommand from the source eNB. The WTRU initiates reception and processingof a primary broadcast channel (P-BCH) at the target cell afterreceiving the handover command. The WTRU then sends a random accesspreamble to the target eNB, receives a random access response from thetarget eNB, and sends a handover complete message to the target eNB. Thereception and processing of the P-BCH may be initiated immediately afterreceiving the handover command or after sending the handover completemessage. The WTRU may initiate a radio link recovery procedure on acondition that a target cell system frame number (SFN) is not acquiredafter a pre-determined period of time. The WTRU may apply defaultconfiguration or source cell configuration in the target cell until atarget cell SFN and/or P-BCH information are acquired.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein;

FIG. 1 is a signaling diagram of a handover process in the 3GPP LTEnetwork;

FIG. 2 is a signaling diagram of an example process in accordance withthe second embodiment;

FIG. 3 is a signaling diagram of an example process in accordance withan alternative to the second embodiment;

FIG. 4 is a flow diagram of an example process for performing a mediumaccess control (MAC) reset and activating DRX and/or semi-persistentscheduling (SPS) in the target cell in accordance with the thirdembodiment; and

FIG. 5 is a block diagram of an example WTRU and an example eNB.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “WTRU” includes but is notlimited to a user equipment (UE), a mobile station, a fixed or mobilesubscriber unit, a pager, a cellular telephone, a personal digitalassistant (PDA), a computer, or any other type of user device capable ofoperating in a wireless environment. When referred to hereafter, theterminology “eNB” includes but is not limited to a base station, aNode-B, a site controller, an access point (AP), or any other type ofinterfacing device capable of operating in a wireless environment.

In accordance with a first embodiment, a new handover command format isdefined. The new handover command format reduces the handoverinterruption time, which is defined as the difference between the time aWTRU receives the handover command and the time the WTRU resumes itsuplink and downlink data transmission and reception in the target cell.

In order for the WTRU to perform normal operation (such as datatransmission, reception and DRX) in the target cell, the WTRU needs toknow cell-specific system information carried on a P-BCH and a D-BCH.However, reading P-BCH (with a transmission time interval (TTI) of 40 msrepeated 4 times) and D-BCH (with scheduling units of 160 and 320 ms)will increase the handover interruption time dramatically. In accordancewith the first embodiment, the cell specific system information carriedon the P-BCH and the D-BCH in the target cell is included in thehandover command. This information may be provided by the target eNB tothe source eNB in the handover request acknowledgement message, (e.g.,included in the transparent container of the handover requestacknowledgement).

The cell-specific system information included in the handover commandmay be at least one of the following:

(1) Downlink system bandwidth;

(2) Physical control format indicator channel (PCFICH) information;

(3) Physical HARQ indicator channel (PHICH) information, (e.g., PHICHduration and PHICH resource size);

(4) Signaling of reference signal transmit power and power scaling ofthe reference signal to other data/control sub-carriers;

(5) RACH configuration: Information of dedicated preamble reserved forthe WTRU in the target cell (validity timer of the dedicated preamble isprovided for both synchronous and asynchronous networks) andcontention-based RACH information (optional);

(6) Information for uplink reference signals (frequency hopping);

(7) Information for sounding reference signals (location);

(8) Physical uplink control channel (PUCCH) reference signal sequencehopping (same for positive acknowledgement (ACK)/negativeacknowledgement (NAK) and/or channel quality indicator (CQI));

(9) Physical uplink shared channel (PUSCH) hopping: semi-staticconfiguration of two hopping modes (inter and intra-sub-frame orinter-sub-frame only hopping) on a cell specific basis;

(10) Uplink power control (cell specific) parameters;

(11) DRX related parameters in the target cell (optional);

(12) Start time of new DRX cycle in the target cell (optional);

(13) System frame number (optional): either full SFN of the target cellor an SFN difference between the source and target cells;

(14) Number of transmit antennas at the target eNB (optional since thismay be blindly detected by the WTRU during cell search);

(15) Multimedia broadcast multicast service single frequency network(MBSFN)-related parameters (optional);

(16) Neighboring cells list (optional);

(17) Configuration information for semi-persistent scheduling (SPS) inthe target cell;

(18) Uplink and/or downlink persistent scheduling parameters (optional);and

(19) Uplink ACK/NACK resource due to downlink persistent scheduling(optional).

Alternatively, the above cell-specific information, (i.e., handoverparameters), may be defined with one or more set of “default” values,and the target eNB may determine which one of the pre-defined sets ofvalues may be used by the WTRU and send only the index to the determinedset of default values for a very compact signalling.

Alternatively, a special system information block (SIB) format may beprovided for predefined handover parameter values (parameters as definedabove) with the scope of one or more public land mobile network (PLMN)(similar to the multiple PLMNs contained in the master information block(MIB) or other SIBs as for the network sharing purpose or just to aparticular PLMN), such that the network/service provider, (i.e., thePLMN owner), may predefine the necessary handover values (one or moresets) for the WTRU to acquire before the handover. The eNBs maybroadcast such an SIB. The handover command may then pass only the indexto the WTRU for the handover parameters to the target eNB.

The WTRU may indicate or report its acquisition of handover parametersfrom the SIB to the network in one of its uplink messages (such as anRRC reconfiguration complete message or an RRC measurement reportmessage, etc). One bit is enough for this purpose.

The network may decide which way the handover parameter values will besent to the WTRU in the handover command, either a complete new set ofvalues, an index to the default value set, or an index to a set of thepredefined value sets in the SIB broadcast by the eNB.

In accordance with a second embodiment, a WTRU immediately startsreceiving and processing the P-BCH and the D-BCH after receiving thehandover command (without SFN information) from the source eNB. FIG. 2is a signaling diagram of an example process 200 in accordance with thesecond embodiment. The WTRU sends a measurement report in accordancewith the rules set by system information, specification, etc. (step202). The source eNB makes a handover decision based on the measurementreport and issues a handover request message to the target eNB passingnecessary information to prepare the handover at the target eNB (step204). The target eNB decides to admit the WTRU and sends a handoverrequest acknowledgement message to the source eNB (step 206). Thehandover request acknowledgement message includes a transparentcontainer to be sent to the WTRU as an RRC message. The source eNB sendsa handover command to the WTRU (step 208).

After receiving the handover command (without SFN information) from thesource eNB, the WTRU immediately starts receiving and processing theP-BCH and the D-BCH (step 210). The WTRU synchronizes to the target celland sends a random access preamble following a contention-free procedureif a dedicated RACH preamble was indicated in the handover command orfollowing a contention-based RACH procedure if no dedicated RACHpreamble was indicated in the handover command (step 212). The receptionof P-BCH and D-BCH may start before the WTRU may transmit the RACHaccess preamble since the WTRU may need to wait for a random accessopportunity (1 sub-frame out of 10 or 20 sub-frames). Since the physicalresources of the P-BCH and the D-BCH are different than those of eNBmessage, (i.e., RACH response), during RACH procedure, the WTRU mayreceive and process both without any problem. The target eNB sends arandom access response to the WTRU (step 214). The WTRU then sends ahandover complete message to the target eNB (step 216). A normaloperation starts between the WTRU and the target eNB thereafter (step218).

The target eNB may assume that the WTRU already acquired the target cellSFN, P-BCH and D-BCH K sub-frames after the WTRU receives the handovercommand, and start normal operations for the WTRU. The period of time toacquire the target cell SFN may be less than the P-BCH and D-BCHinformation. Before that, the normal operations may not be started bythe target eNB for the WTRU. These normal operations include, but arenot limited to, DRX cycle, L1 feedback, dynamic and semi-persistent datatransmission and reception, timing alignment, RACH process, or the like.

The WTRU may provide implicit or explicit signaling to inform the targeteNB of when the target cell SFN and/or BCH information is acquired.Alternatively, if the WTRU fails to receive target cell SFN and P-BCHand detect P-BCH timing successfully after K sub-frames, the WTRU maytreat it as radio link failure and start radio link recovery procedure.

A default mode of operation may be applied in the target cell until theWTRU acquires target cell SFN and/or BCH information after sending thehandover complete message. Generally, the functions, (e.g., DRX), thatare affected by not having the target cell SFN and/or other systeminformation on the target cell at the time of handover may be disableduntil the target cell information is acquired and applied, oralternatively, may operate as it would have in the source cell and thenswitch when the target cell information is acquired and applied. Forexample, DRX operation may be disabled, and L1 feedback may not begenerated or may be ignored.

FIG. 3 is a signaling diagram of an example process 300 in accordancewith an alternative to the second embodiment. The WTRU sends ameasurement report in accordance with the rules set by systeminformation, specification, etc. (step 302). The source eNB makes ahandover decision based on the measurement report and issues a handoverrequest message to the target eNB passing necessary information toprepare the handover at the target eNB (step 304). The target eNBdecides to admit the WTRU and sends a handover request acknowledgementmessage to the source eNB (step 306). The handover requestacknowledgement message includes a transparent container to be sent tothe WTRU as an RRC message. The source eNB sends a handover command tothe WTRU (step 308).

Upon receipt of the handover command, the WTRU detaches from the sourcecell and synchronizes to the target cell and sends a RACH accesspreamble to the target eNB following a contention-free procedure if adedicated RACH preamble was indicated in the handover command orfollowing a contention-based RACH procedure if no dedicated preamble wasindicated in the handover command (step 310). The target eNB sends arandom access response with uplink allocation and timing advance valuefor the WTRU (step 312). The WTRU then sends a handover complete messageto the target eNB (step 314). After sending the handover completecommand to the target eNB, the WTRU may immediately start receiving andprocessing the P-BCH and the D-BCH on the target cell (step 316). AfterK sub-frames from the handover complete message, a normal operation maystart between the WTRU and the target eNB (step 318).

A default mode of operation may be applied in the target cell until theWTRU acquires target cell SFN and/or BCH information after sending thehandover complete message. Generally, the functions, (e.g., DRX), thatare affected by not having the target cell SFN and/or other systeminformation on the target cell at the time of handover may be disableduntil the target cell information is acquired and applied, oralternatively, may operate as it would have in the source cell and thenswitch when the target cell information is acquired and applied. Forexample, DRX operation may be disabled, and L1 feedback may not begenerated or may be ignored.

If the DRX related parameters are provided only in the SIB in the targetcell, the WTRU may use the DRX parameters from the source cell andcontinue with DRX operation until the VI/TRU reads the SFN on the targetcell. Alternatively, the WTRU may not apply DRX until the WTRU reads DRXparameters from the system information on the target cell.

If there is no new SFN value when a WTRU enters the target cell, thetarget eNB may reconfigure the SPS parameters, such as periodicities,HARQ process or radio resources. Alternatively, since an MIB may bereceived within 16 ms and the interruption may be short, SPS may bedisabled until the WTRU gets the SFN information on the target cell.

The WTRU may keep the configuration for DRX and SPS as used in thesource cell. The source eNB scheduler may make an implicit or explicitindication of when the WTRU switches to the new configuration to thetarget eNB. The source eNB may inform the target eNB of the DRX/SPSactivity patterns that will be in effect. The target eNB may reject thesource cell DRX/SPS activity patterns and have the WTRU de-activateuntil the target cell system information is acquired.

In accordance with a third embodiment, a WTRU may discard or ignore thesource cell configuration, (e.g., SPS and/or DRX configuration such asSPS semiPersistSchedInterval, DRX cycles, etc), upon a medium accesscontrol (MAC) reset due to handover. Upon reception of the handovercommand from the source eNB, the WTRU performs a MAC reset and maydiscard or ignore the source cell configuration.

Alternatively, the WTRU may keep and continue with the source cellconfigurations. The WTRU MAC entity may preserve the source cellconfiguration during the MAC reset. Alternatively, the WTRU MAC entitydiscards the source cell configuration due to the MAC reset, but theWTRU RRC entity may preserve the source cell configuration andre-configure the MAC entity with the source cell configuration followingthe handover, (e.g., once or after the MAC reset procedure iscompleted).

The operations in the target cell, (e.g., SPS and/or DRX operations),may be activated by eNB signaling to the WTRU in the source cell, by eNBsignaling to the WTRU in the target cell, or in accordance with apre-defined rule.

FIG. 4 is a flow diagram of an example process 400 for performing a MACreset and activating DRX and/or SPS in the target cell in accordancewith the third embodiment. A WTRU receives a handover command from thesource eNB and performs a MAC reset (step 402). The WTRU deactivates DRXand/or SPS upon or due to MAC reset or during the execution of thehandover procedure (step 404). The WTRU discards or disregards thesource cell DRX and/or SPS configurations upon or due to MAC reset (step406). The WTRU receives a first signaling message, (e.g., an RRCmessage, or any L2 or L3 message), indicating the target cell DRX and/orSPS configurations directly from the target eNB in the target cell (step408). The target eNB was made aware of the source cell DRX and/or SPSconfigurations for the WTRU via a signaling message sent from the sourceeNB to the target eNB, (e.g., in the handover request message or asubsequent message). The WTRU receives a second signaling message,(e.g., a PDCCH signal, an RRC message, or any L2 or L3 message),indicating activation of DRX and/or SPS, or when to activate DRX and/orSPS, directly from the target eNB in the target cell (step 410). Thefirst and the second signaling messages may be sent simultaneously orseparately, or may be combined in one message. The WTRU then activatesDRX and/or SPS in the target cell in accordance with the target cellconfiguration and activation information (step 412).

The target cell DRX and/or SPS configuration provided in the firstsignaling message may be interpreted in a following way. The absence ofa DRX and/or SPS configuration IE in the first signaling message isinterpreted by the WTRU as an indication to preserve and continue withthe existing DRX and/or SPS configurations. The presence of a DRX and/orSPS configuration IE in the first signaling message is interpreted bythe WTRU to reconfigure its DRX and/or SPS configurations in accordancewith the configuration included in the first signaling message. Anindication bit may be included in the first signaling message toindicate to the WTRU whether the WTRU should preserve and continue withthe existing DRX and/or SPS configurations or disregard the existingconfiguration.

Instead of receiving the target cell DRX and/or SPS configurations viathe first signaling message from the target eNB, the target cell DRXand/or SPS configurations may be received via the handover command. Inthe handover command's transparent container sent from the target eNB tothe source eNB, the target eNB indicates the DRX and/or SPSconfigurations. The target eNB was made aware of the source eNB DRXand/or SPS configurations via a signaling message sent from the sourceeNB to the target eNB, (e.g., in the handover request message or in asubsequent message). The absence of a DRX and/or SPS configuration IE inthe handover command is interpreted by the WTRU as an indication topreserve and continue with the existing DRX and/or SPS configurationsand the presence of the DRX and/or SPS configuration IE in the handovercommand is interpreted by the WTRU to reconfigure its DRX and/or SPSconfigurations in accordance with the included configuration parameters.An indication bit may be included in the handover command to indicate tothe WTRU whether the WTRU should preserve and continue with the existingDRX and/or SPS configurations, or disregard the existing configuration.

The WTRU may decide when to activate DRX and/or SPS, (e.g., at or aftera specific time or SFN), based on a pre-defined criteria, instead of thesecond signaling message from the target eNB.

It should be noted that the example process described in FIG. 4 mentionboth DRX and SPS together (in order to avoid text repetition), but itmay be applied separately to the DRX independent of SPS, to the uplinkSPS independent of DRX and downlink SPS, to downlink SPS independent ofDRX or uplink SPS, or to any other functions.

FIG. 5 is a block diagram of an example WTRU 510 and an eNB 520. TheWTRU 510 is in communication with the eNB 520 and both are configured toperform a method of performing a handover in an E-UTRAN. In addition tothe components that may be found in a typical WTRU, the WTRU 510includes a transmitter 512, a receiver 514, and a processor 516, amemory 518 and an antenna 519. The memory 518 is provided to storesoftware including operating system, application, etc. The processor 516is provided to perform, alone or in association with the software, amethod of performing a handover in accordance with one of theembodiments disclosed above. The transmitter 512 and the receiver 514are in communication with the processor 516. The antenna 519 is incommunication with both the transmitter 512 and the receiver 514 tofacilitate the transmission and reception of wireless data.

In addition to the components that may be found in a typical eNB, theeNB 520 includes a transmitter 522, a receiver 524, a processor 526, andan antenna 528. The processor 526 is provided to perform a method ofperforming a handover in accordance with one of the embodimentsdisclosed above. The transmitter 522 and the receiver 524 are incommunication with the processor 526. The antenna 528 is incommunication with both the receiver 524 and the transmitter 522 tofacilitate the transmission and reception of wireless data.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB)module.

1.-2. (canceled)
 21. A method implemented in a wireless transmit/receiveunit (WTRU) for performing a handover from a source cell to a targetcell, the method comprising: initiating reception of a primary broadcastchannel (P-BCH) of the target cell after receiving a handover commandfrom an evolved Node B (eNB) associated with the source cell; sending arandom access preamble to an eNB associated with the target cell, therandom access preamble being sent using a contention-based random accesschannel (RACH) procedure on condition that no dedicated RACH preamble isindicated in the handover command; receiving a random access responsefrom the eNB associated with the target cell; applying a first mode ofoperation prior to acquiring a system frame number (SFN) of the targetcell, the first mode of operation causing the WTRU to refrain fromutilizing the SFN of the target cell and causing the WTRU to refrainfrom using discontinuous reception (DRX) operation in the target cell;and applying a second mode of operation upon acquiring the SFN of thetarget cell, the second mode of operation causing the WTRU to take intoaccount the SFN of the target cell and causing the WTRU to enable theDRX operation in the target cell.
 22. The method of claim 21, whereinthe sending the random access preamble further includes using acontention-free RACH procedure on condition that a dedicated RACHpreamble is indicated in the handover command.
 23. The method of claim21, further comprising resetting medium access control (MAC) in responseto receiving the handover command.
 24. The method of claim 21, whereinthe first mode of operation further causes the WTRU to refrain fromutilizing semi-persistent scheduling (SPS) in the target cell.
 25. Themethod of claim 24, wherein the second mode of operation further causesthe WTRU to enable the SPS in the target cell.
 26. A wirelesstransmit/receive unit (WTRU) comprising: a processor, the processorconfigured at least to: initiate reception of a primary broadcastchannel (P-BCH) of a target cell after receiving a handover command froman evolved Node B (eNB) associated with a source cell; and atransceiver, the transceiver configured at least to: send a randomaccess preamble to an eNB associated with the target cell, the randomaccess preamble being sent using a contention-based random accesschannel (RACH) procedure on condition that no dedicated RACH preamble isindicated in the handover command; and receive a random access responsefrom the eNB associated with the target cell, the processor beingfurther configured to: apply a first mode of operation prior toacquiring a system frame number (SFN) of the target cell, the first modeof operation including a configuration causing the WTRU to refrain fromutilizing the SFN of the target cell and causing the WTRU to refrainfrom utilizing discontinuous reception (DRX) operation in the targetcell; and apply a second mode of operation upon acquiring the SFN of thetarget cell, the second mode of operation including a configurationcausing the WTRU to take into account the SFN of the target cell andcausing the WTRU to enable the DRX operation in the target cell.
 27. TheWTRU of claim 26, wherein the transceiver is further configured suchthat the sending the random access preamble includes using acontention-free RACH procedure on condition that a dedicated RACHpreamble is indicated in the handover command.
 28. The WTRU of claim 26,wherein the processor is further configured to reset medium accesscontrol (MAC) in response to receiving the handover command.
 29. TheWTRU of claim 26, wherein the processor is further configured such thatthe configuration of the first mode further causes the WTRU to refrainfrom using semi-persistent scheduling (SPS) in the target cell.
 30. TheWTRU of claim 29, wherein the processor is further configured such theconfiguration of the second mode further causes the WTRU to enable theSPS in the target cell.
 31. A method implemented in a wirelesstransmit/receive unit (WTRU) for performing a handover from a sourcecell to a target cell, the method comprising: initiating reception of aprimary broadcast channel (P-BCH) of the target cell after receiving ahandover command from an evolved Node B (eNB) associated with the sourcecell; sending a random access preamble to an eNB associated with thetarget cell, the random access preamble being sent using acontention-based random access channel (RACH) procedure on conditionthat no dedicated RACH preamble is indicated in the handover command;receiving a random access response from the eNB associated with thetarget cell; applying a first mode of operation prior to acquiring asystem frame number (SFN) of the target cell, the first mode ofoperation causing the WTRU to refrain from utilizing the SFN of thetarget cell and causing the WTRU to refrain from using Layer 1 (L1)feedback in the target cell; and applying a second mode of operationupon acquiring the SFN of the target cell, the second mode of operationcausing the WTRU to take into account the SFN of the target cell andcausing the WTRU to enable the L1 feedback in the target cell.
 32. Themethod of claim 31, wherein the sending the random access preamblefurther includes using a contention-free RACH procedure on conditionthat a dedicated RACH preamble is indicated in the handover command. 33.The method of claim 31, further comprising resetting medium accesscontrol (MAC) in response to receiving the handover command.
 34. Themethod of claim 31, wherein the first mode of operation further causesthe WTRU to refrain from utilizing semi-persistent scheduling (SPS) inthe target cell.
 35. The method of claim 34, wherein the second mode ofoperation further causes the WTRU to enable the SPS in the target cell.36. A wireless transmit/receive unit (WTRU) comprising: a processor, theprocessor configured at least to: initiate reception of a primarybroadcast channel (P-BCH) of a target cell after receiving a handovercommand from an evolved Node B (eNB) associated with a source cell; anda transceiver, the transceiver configured at least to: send a randomaccess preamble to an eNB associated with the target cell, the randomaccess preamble being sent using a contention-based random accesschannel (RACH) procedure on condition that no dedicated RACH preamble isindicated in the handover command; and receive a random access responsefrom the eNB associated with the target cell, the processor beingfurther configured to: apply a first mode of operation prior toacquiring a system frame number (SFN) of the target cell, the first modeof operation including a configuration causing the WTRU to refrain fromutilizing the SFN of the target cell and causing the WTRU to refrainfrom utilizing Layer 1 (L1) feedback in the target cell; and apply asecond mode of operation upon acquiring the SFN of the target cell, thesecond mode of operation including a configuration causing the WTRU totake into account the SFN of the target cell and causing the WTRU toenable the L1 feedback in the target cell.
 37. The WTRU of claim 36,wherein the transceiver is further configured such that the sending therandom access preamble includes using a contention-free RACH procedureon condition that a dedicated RACH preamble is indicated in the handovercommand.
 38. The WTRU of claim 36, wherein the processor is furtherconfigured to reset medium access control (MAC) in response to receivingthe handover command.
 39. The WTRU of claim 36, wherein the processor isfurther configured such that the configuration of the first mode furthercauses the WTRU to refrain from using semi-persistent scheduling (SPS)in the target cell.
 40. The WTRU of claim 39, wherein the processor isfurther configured such the configuration of the second mode furthercauses the WTRU to enable the SPS in the target cell.